1. Field of the Invention
The present invention concerns a molding method and an injection-molding machine for compositing an injection molded primary molding and an injection-molded secondary molding of different material resin by a secondary cavity mold, by transferring rotating the injection-molded primary molding together with a core mold to the secondary cavity mold, and holding in contact with the cavity mold surface by a holding pin.
2. Detailed Description of the Prior Art
For the molding of a composite-molding made of two kinds of material resins different in color or material (called different material resins), a method of inserting a molding molded by another injection machine into a cavity of a mold for molding the product main body and molding integrally by injection, and a so-called dichromatic molding method of molding primarily the portion of character and the main body and then molding secondarily the surrounding of characters with a different material resin are known.
In the insert molding method, a resin refilling space is secured in the cavity by holding the insert by a holding pin. As a result, if the holding pin is extracted after cooling and solidification of the resin, the pin trace remains as a hole on the surface of the molding. This pin trace often constitutes an undesirable defect for a product and, as a solution, the holding pin extraction timing is advanced before the resin solidification, and the refilling of the unfilled region by the holding pin with resin is performed by a secondary injection filling with resin from an injection unit, so that the pin trace may not remain.
However, the insert is only supported by a fluid resin and not fixed, and is in a state to move easily with the resin due to the regressive displacement of the holding pin. Therefore, if the cavity is filled with resin for refilling from the injection unit, the insert shifts out of the set position by moving through the resin pressure in the resin flow direction due to the refilling pressure, i.e., in the counter-gate direction, often making the product inferior.
In the dichromatic method, if the primary mold has characters or numerals in a form having a surrounding area (for example, A, B, P, 8, 9, 0) partially protruding on the top surface thereof, it becomes necessary to dispose a gate at two points or three points of a recess closed by the surrounding area and a cavity, to provide a hot runner for these gate in the mold, making the structure of the secondary cavity mold complex. Moreover, some of small composite products make the molding impossible given the restriction of the gate position.
For a solution means, it may be considered to form a communicating hole in the recess of the primary molding by a projection pin to hold the primary molding in contact with a cavity mold surface by a holding pin, similar to the case of insert molding, and fill both the cavity inside and the recess with resin from a gate of one point through the communicating hole. However, defects due to the holding pin trace or lateral-shift of the primary molding, drawbacks of the aforementioned insert molding, are not resolved.
The present invention, made in order to solve the aforementioned problems of the prior art, has as an object to provide a novel method and an injection-molding machine preventing the primary molding from displacing under the resin pressure during the refilling, and allowing to form a composite-molded product free from defect, by making it possible to fill the closed recess and the cavity with resin through a gate of a single point, even when composite-moldings are formed successively with different material resin by adopting the dichromatic molding method, and refilling portions not filled with resin due to the holding pin by pressing resin by the pushing pin after the injection filling.